The present invention relates to clustered computer systems and, more particularly, to methods for mirroring disk drives within a network.
The increased reliance by business on On-Line Transaction Processing and Decision Support Systems has increased the demand for high availability systems since these systems are critical to the functioning of day-to-day activities in many businesses. These systems are not only essential for the support of normal daily operations, but they also store critically important customer and corporate data. Continuous availability is no longer an ideal; it is a necessity for many companies. Longer workdays, expansion into new markets and customer demand for more efficient service create an expanded requirement for increased system availability. Users are demanding a means of ensuring very high availability of their applications and the access to data that permits them to accomplish their tasks and provide the highest levels of customer service. Interruption of workflow due to system failure is expensive and it can cause the loss of business. The need to increase computer system availability is becoming one of businesses key concerns.
Implementation of client/server computing is growing throughout today""s businessesxe2x80x94for key business applications as well as electronic mail, distributed databases, file transfer, retail point-of-sale, inter-networking, and other applications. It is possible for companies to gain competitive advantages from client/server environments by controlling the cost of the technology components through economies of scale and the use of clustered computing resources. There is a boost in productivity when businesses have high availability and easy access to information throughout the corporate enterprise.
Computer system availability and reliability are improved when multiple servers are utilized together with a xe2x80x9cfail-overxe2x80x9d scheme such as provided by NCR Corporation""s LifeKeeper product. In such a system, should one server fail, the functions and applications associated with the failed server are transferred to one or more of the remaining operational or standby servers.
An important component of a high-availability client/server system is a reliable, fault-tolerant data storage system. In some networked or xe2x80x9cclusteredxe2x80x9d multiple server arrangements, the physical data storage system may be a shared RAID (Redundant Array of Inexpensive Disks) disk array system, or a shared pair of disk drives or disk arrays operating in a mirrored arrangement.
A computer system including multiple servers and a pair of shared disk drives is shown in FIG. 1. FIG. 1 provides a diagram of clustered or networked computers having a primary server 101 and a secondary server 103 in a fail-over pair arrangement. Primary server 101 is the preferred application server of the pair, and secondary server 103 preferably provides fail-over protection for the primary server. The primary and secondary servers are coupled through a network bus system 105 to a plurality of client computers 107 though 109. The primary and secondary servers 101 and 103 each share access to a pair of disk storage devices 111 and 113. Disk storage devices 111 and 113 are SCSI (Small Computer Systems Interface) disk drives or disk arrays connected to servers 101 and 103 through a pair of SCSI busses 115 and 117.
Disk storage devices 111 and 113 are two equal-capacity storage devices that mirror each other. Each storage device contains a duplicate of all files contained on the other storage device, and a write or update to one storage device updates both devices in the same manner. In the event that either storage device fails, the data contained therein remains available to the system from the operational mirror storage device.
In other client/server arrangements, the physical storage devices for the primary and secondary servers may be separate, non-shared, physical storage devices. Implementation of a non-shared, storage device mirroring process over a network is a more complicated process than mirroring with a pair of shared storage devices since some hardware clustering technologies rely on the physical state of the attached storage device to manage the cluster. Microsoft Corporation""s Cluster Server product (MSCS), for example, uses the SCSI Reserve/Release protocol to manage the ownership of shared disks between members of the cluster. Without shared storage devices, and no SCSI control of the underlying physical disk drives, then there is no cluster with MSCS. Furthermore, since the SCSI Reserve/Release protocol operates with physical disk drives, it would not be possible to mirror a storage unit smaller than the physical disk drive, such as a partition.
In order to implement a non-shared, storage device mirroring process over a network, the clustering technology that is relying on a shared physical storage device must be xe2x80x9cfooledxe2x80x9d into believing that there is a shared device.
A network based file system volume replication scheme where the contents of the file system stored on a primary physical storage media are also copied to a secondary physical storage media is commercially available from NCR Corporation, assignee of the present application, under the product name xe2x80x9cExtended Mirroringxe2x80x9d.
It is therefore an object of the present invention to provide a new and useful method and mechanism for mirroring storage devices over a network.
It is another object of the present invention to provide such a method for mirroring non-shared storage devices.
It is yet another object of the present invention to provide a new and useful method and mechanism for mirroring non-shared storage device state within a clustered system by representing the storage device as a shared drive to the cluster engine.
It is still a further object of the present invention to provide a new and useful method and mechanism for mirroring disk partitions over a network.
There is provided, in accordance with the present invention, a system for mirroring data and disk drive device state over a network between a source computer including a first non-shared storage volume and a target computer including a second non-shared storage volume.
The source and target storage volumes reside on first and second physical disk drive devices, respectively. The source computer includes a file system mirror driver, installed above the device driver for the first disk drive device, for capturing write requests directed to the first storage volume and transmitting the write requests to the target computer. A state filter driver, also installed above the device driver for the first disk drive device, examines the write requests directed to the first storage volume to determine a device state for the first physical disk drive and transmits the device state to the target computer.
The target computer includes a device state storage device; a file system mirror driver for receiving the write requests from the source computer and directing the write requests to the second storage volume; and a state mirror driver for receiving the device state from the source computer and storing the device state within the device state storage device.
The above and other objects, features, and advantages of the present invention will become apparent from the following description and the attached drawings.